1. Field of the Invention
The present invention relates to an over write capable magnetooptical recording medium having a controlled exchange coupling force between magnetic layers.
2. Related Background Art
In recent years, many efforts have been made to develop an optical recording/reproduction method, an optical recording apparatus and a medium used therefor, which can satisfy various requirements including high density, large capacity, high speed access, and high recording/reproduction speed.
Of various optical recording/reproduction methods, the magnetooptical recording/reproduction method is most attractive due to its unique advantages that information can be erased after use and new information can be written thereon.
A recording medium used in a magnetooptical recording/reproduction method has a perpendicular magnetic layer or layers as a recording layer. The magnetic layer comprises, for example, amorphous GdFe, GdCo, GdFeCo, TbFe, TbCo, TbFeCo, and the like. Concentrical or spiral tracks are formed on the recording layer, and data is recorded on the tracks. Note that in this specification, one of the "upward" and "downward" directions of magnetization with respect to a film surface is defined as an "A direction" and the other one is defined as a "non-A direction". Data to be recorded is binarized in advance, and is recorded by a mark or bit (B.sub.1) having "A-directed" magnetization and a mark or bit (B.sub.0) having "non-A-directed" magnetization. These marks B.sub.1 and B.sub.0 correspond to "1" and "0" levels of a digital signal, respectively. However, in general, the direction of magnetization of the recording tracks can be aligned in the "non-A direction" by applying a strong bias field before recording. This processing is called "initialization". Thereafter, the mark (B.sub.1) having "A-directed" magnetization is formed on the tracks. Data is recorded in accordance with the presence/absence and/or a mark length of the mark (B.sub.1).